Effects of Structural and Microstructural Features on the Total Scattering Pattern of Nanocrystalline Materials.

Atomic- and nanometer-scale features of nanomaterials have a strong influence on their chemical and physical properties and a detailed description of these elements is a crucial step in their characterization. Total scattering methods, in real and reciprocal spaces, have been established as fundamental techniques to retrieve this information. Although the impact of microstructural features, such as defectiveness of different kinds, has been extensively studied in reciprocal space, disentangling these effects from size- and morphology-induced properties, upon downsizing, is not a trivial task. Additionally, once the experimental pattern is Fourier transformed to calculate the pair distribution function, the direct fingerprint of structural and microstructural features is severely lost and no modification of the histogram of interatomic distances derived therefrom is clearly discussed nor considered in the currently available protocols. Hereby, starting from atomistic models of a prototypical system (cadmium selenide), we simulate multiple effects on the atomic pair distribution function, obtained from reciprocal space patterns computed through the Debye scattering equation. Size and size dispersion effects, as well as different structures, morphologies, and their interplay with several kinds of planar defects, are explored, aiming at identifying the main (measurable and informative) fingerprints of these features on the total scattering pattern in real and reciprocal spaces, highlighting how, and how much, they become evident when comparing different cases. The results shown herein have general validity and, as such, can be further extended to other classes of nanomaterials.

Microfluidic Crystallization of Surfactant-Free Doped Zinc Sulfide Nanoparticles for Optical Bioimaging Applications.

The room-temperature controlled crystallization of monodispersed ZnS nanoparticles (average size of 5 nm) doped with luminescent ions (such as Mn2+, Eu3+, Sm3+, Nd3+, and Yb3+) was achieved via a microfluidic approach. The preparation did not require any stabilizing ligands or surfactants, minimizing potential sources of impurities. The synthesized nanomaterials were characterized from a structural (XRD and XAS at lanthanide L3 edges), morphological (TEM), and compositional (XPS, ICP-MS) perspective, giving complementary information on the materials' features. In view of potential applications in the field of optical bioimaging, the optical emission properties of the doped nanoparticles were assessed, and samples showed strong luminescent properties while being less affected by self-quenching mechanisms. Furthermore, in vitro cytotoxicity experiments were conducted, showing no negative effects and evidencing the appeal of the synthesized materials for potential applications in the field of optical bioimaging.

Ligand-free ZnS nanoparticles: as easy and green as it gets.

The controlled nucleation and crystallization of small pure sphalerite ZnS nanoparticles was achieved under batch and continuous flow conditions at low temperature, in water and without the use of any stabilizing ligand. The obtained nanoparticles displayed a narrow size distribution and high specific surface area. Moreover, the synthesis was suitable to directly obtain stable water-based suspensions and the products were found to be active photocatalysts for the hydrogen evolution reaction.

Exploring the Phase-Selective, Green, Hydrothermal Synthesis of Upconverting Doped Sodium Yttrium Fluoride: Effects of Temperature, Time, and Precursors.

The aim of this work was i) to develop a hydrothermal, low-temperature synthesis protocol affording the upconverting hexagonal phase NaYF4 with suitable dopants while adhering to the "green chemistry" standards and ii) to explore the effect that different parameters have on the products. In optimizing the synthesis protocol, short reaction times and low temperatures (below 150 °C) were considered. Yb3+ and Er3+ ions were chosen as dopants for the NaYF4 material. Within the context of the second goal, parameters including nature of the precursors, treatment temperature, and treatment time were investigated to afford a pure hexagonal crystalline phase, both in the doped and undoped materials. To fully explore the synthesis results, the prepared materials were characterized from a structural (XRD), compositional (XPS, ICP-MS), and morphological (SEM) point of view. The upconverting properties of the compounds were confirmed by photoluminescence measurements.

Thermal Evolution of ZnS Nanostructures: Effect of Oxidation Phenomena on Structural Features and Photocatalytical Performances.

ZnS nanosystems are being extensively studied for their possible use in a wide range of technological applications. Recently, the gradual oxidation of ZnS to ZnO was exploited to tune their structural, electronic, and functional properties. However, the inherent complexity and size dependence of the ZnS oxidation phenomena resulted in a very fragmented description of the process. In this work, different-sized nanosystems were obtained through two different low temperature wet chemistry routes, namely, hydrothermal and inverse miniemulsion approaches. These protocols were used to obtain ZnS samples consisting of 21 and 7 nm crystallites, respectively, to be used as reference material. The obtained samples were then calcinated at different temperatures, ranging from 400 to 800 °C toward the complete oxidation of ZnO, passing through the coexistence of the two phases (ZnS/ZnO). A thorough comparison of the effects of thermal handling on ZnS structural, chemical, and functional evolution was carried out by TEM, XRD, XAS, XPS, Raman, FT-IR, and UV-Vis. Finally, the photocatalytic activity in the H2 evolution reaction was also compared for selected ZnS and ZnS/ZnO samples. A correlation between size and the oxidation process was observed, as the smaller nanosystems showed the formation of ZnO at lower temperature, or in a larger amount in the case of the ZnS and ZnO co-presence. A difference in the underlying mechanism of the reaction was also evidenced. Despite the ZnS/ZnO mixed samples being characterized by an increased light absorption in the visible range, their photocatalytic activity was found to be much lower.